On Thursday, its revenue product manager Abhishek Shrivastava said in a blog post that the pilot was complete and that it was now dishing up "tailored audiences" to advertisers.

The company explained:

With tailored audiences you can reach users on Twitter who have shown interest in your brand or your category even away from Twitter. Let’s say a hotel brand wants to advertise a promotion on Twitter and they’d prefer to show their ad to travel enthusiasts who have recently visited their website.

To get the special offer to those people who are also on Twitter, the hotel brand may share with us browser-related information (browser cookie ID) through an ads partner. We can then match that information to Twitter accounts in order to show the matched users a Promoted Tweet with the travel deal. The end result is a highly relevant and useful message for the user.

Advertisers will continue to receive the same reports that include how many users saw or clicked on an ad, without identifying who saw it or clicked on it.

The tech is used widely across websites that function as free content ad networks - such as Facebook.

But concerns have been expressed about cookies, with some considering it to be an invasion of privacy when browsing to sites online.

Twitter noted the nervousness among some folk by pointing out that its users can opt out of its ad-tracking methods by unchecking the "promoted content" box in its privacy settings.

It added that it "will not receive browser-related information (a browser cookie ID) from our ads partners for tailoring ads if users have Do Not Track enabled in their browser." ®